Corrosion Resistance Without Hexavalent Chromium―New Zinc Plating Systems

摘要

Times are changing fast in the world of zinc-plated finishes as industry and consumer groups impose ever-increasing demands on product quality, cost, and safety. Electroplated zinc has moved over the past few decades from being a simple plating process applied to steel components to protect against rusting, to a technology comprising a range of zinc and zinc alloy systems to which specially formulated conversion coatings and topcoats can be applied in order to meet specific end-user requirements. Considerable advances have thus been made in improving deposit distribution, corrosion resistance, friction characteristics, etc. by the introduction of these multifunctional coatings. Until now most commercial systems employed conversion coatings based on hexavalent chromium salts in order to achieve the desired corrosion resistance. These conversion coatings are applied to zinc-plated surfaces by immersion in solutions containing chromate or dichromate ions, and serve to delay the formation of zinc corrosion―so-called white rust―and to provide a decorative appearance.